The majority of organic polymers are poor semi-conductors of electricity and therefore have a tendency to accumulate static electrical charge. As such, they cannot be readily used in application areas which require semiconductive properties unless further modified.
Polyisocyanate-based polymers are useful in a wide variety of applications. Some of the applications are more sensitive than others to damage or discomfort caused by the accumulation of static electrical charges and their ultimate discharge. Areas where this may be critical include, for example, packaging of electronic components and medical applications where certain clean room operations require an essentially dust-free environment. Clothing and equipment prepared from or containing polyisocyanate-based polymers may susceptible to the accumulation of static electricity and therefore will attract or be a means of transporting dust into the clean room or dust-free areas.
It is known, for example, to incorporate conductive fillers such as fibers, powders and particles into a polymer to enhance its conductivity and thus reduce its potential to accumulate static electricity. However, loadings of such fillers are often in excess of 15 percent or more to obtain the good electrical semiconductivity or static discharge properties. Such high loadings are not beneficial to the polymer and its physical properties and may, for example, increase its brittleness.
In U.S. Pat. Nos. 4,617,325 and 4,618,630, a means of obtaining polyurethane polymers which can dissipate electrical charge is taught by the use of antistatic additives consisting of ionizable salt in combination with "an enhancer." The enhancer is a certain carboxylic acid ester or salt of a fatty acid or phosphate ester. The incorporation of ionizable salts into a urethane polymer can lead to undesirable properties such as corrosion where the polymer may be in contact with metal surfaces and processing problems in the preparation of the polymer.
It would, therefore, be desirable to provide a polyisocyanate-based polymer which contains no fillers or ionizable salts and yet shows excellent static electrical discharge properties.